In machining devices such as machine tools, positioning accuracy is required to exceed machining accuracy. Recent machining techniques allow for increased machining accuracy, and consequently the required positioning accuracy is also increasing. A highly accurate position measuring device is necessary in order to perform high-accuracy positioning, and linear encoders are known as measuring devices that fulfil this requirement.
The configuration disclosed in FIG. 9 of JP 2007-040873 A, for example, is known as a basic configuration of a publicly known linear encoder. This linear encoder consists of a slider which slides along a glass scale, and a fixed link or the like for mounting on a movable portion of a machine tool or the like. The abovementioned slider comprises a sensor portion which reads displacement, left and right side portion guide rollers provided with leaf springs in order to allow them to slide with little deflection of the glass scale, and lower portion guide rollers.
The abovementioned fixed link is linked via a linking pivot to the slider with the sensor portion, in a state which approaches a floating state by virtue of the urging force of a spring, such that the linear encoder can be provided with the ability to track vibrations from the machine tool.
With the aim of facilitating the exchange of a detecting portion in the length measuring device, JP 07-083647 A discloses a removing and attaching method and removing and attaching jig for a detecting portion in a length measuring device, in which a side end of a case is opened, the removing and attaching jig is installed at said side end, and the detecting portion is moved into and accommodated inside the removing and attaching jig. The removing and attaching jig is separated from the case and is connected to another case, the removing and attaching jig is caused to move and the detecting portion is accommodated inside the other case. This literature also describes that the side end of the case can be opened and closed freely by means of a lid member.
However, the technique in this literature aims to facilitate the exchange of the detecting portion in a length measuring device, and not to facilitate gap adjustment. The side end of the case is opened in order to move the detecting portion into the removing and attaching jig and to accommodate it therein, the removing and attaching jig being mounted at the side end of the opened case. This literature contains no description or suggestion relating to gap adjustment. Further, opening the side end of the case as in this literature results in an opening that is too large, such that the impact of outside air is significant. There is thus the danger that the scale accommodated inside will be exposed to dust, adversely affecting the reading accuracy.